I have a couple of Head Radical TwinTube OS`s and I have noticed for the first time that when one of them is strung the head becomes noticeably wider and shorter than the unstrung frame. It returns to normal when the strings are cut out. The recommended tension for these racquets is 64lbs +-4lbs, and I string the mains with a multi at 63 and the the crosses with a poly at 59. Is this warping normal for any racquet/string job? Is it because I have the mains strung 4lbs tighter than the crosses? I`m guessing its normal and I have just never noticed it before...would appreciate some info. Thanks!